In situ high pressure high temperature experiments in multi-anvil assemblies with bixbyite-type In2O3 and synthesis of corundum-type and orthorhombic In2O3 polymorphs

Our in situ high pressure high temperature experiments in multi-anvil assemblies unambiguously evidence the stability of bixbyite-type c-In2O3 at 6 GPa from room temperature to ca. 600 degrees C. At 5.5 GPa and ca. 1100 degrees C, c-In2O3 reacts with free carbon from the amorphous SiBCN capsule being reduced to metallic indium. The material recovered from the ex situ multi-anvil experiment at 6 GPa and 1100 degrees C using the Mo capsule is inhomogeneous, thereby its phase composition depends on the specimen position from the furnace midline that in turn is characterized by the inhomogeneous temperatures. In the midpoint of the furnace, at the highest temperature point, c-In2O3 completely transforms into a corundum-type rh-In2O3 polymorph that is recovered under ambient conditions, as confirmed by X-ray powder and electron diffraction and Raman spectroscopy. Transmission electron microscopic characterization indicates the growth of single crystals of corundum-type rh-In2O3 with an average crystal size of approximate to 3 m in the specimen part away from the furnace midline. The automated electron diffraction tomography analysis and X-ray powder-diffraction point out at the possible formation of orthorhombic In2O3 polymorphs.